Splice inserts and breaker materials up to now have utilized conventional belt fabrics and some light to mid-weight leno fabrics. Conventional fabrics for belts include plain weaves, rib weaves and crow-foot (broken twill) weaves which have warp cover factors above 75%. These fabrics, while providing needed strength and stability, prevent rubber penetration and, therefore, limit the mechanical bonding by virtue of the high cover factors. Lack of mechanical bonding in severe applications can lead to delamination where the chemical bond cannot tolerate the shear stresses. When a conventional fabric is used as a splice material, shear stresses can cause a cover crack across the belt at the interface of the fabric insert and the carcass fabric/compound. This cracking can also lead to peeling or breaking the splice apart. In splices, fabric fingers are often cut in the insert to dissipate the shear stresses, but the finger can also begin to peel away.
Leno fabrics are not affected by the shear stresses as are conventional fabrics, but they have a weaving limitation. Lenoing mechanisms are simply not made for heavy constructions. The state of the art leno heddles can only lift up to a mid-weight fabric (about 15 oz/yd.sup.2) at most. Even if the mechanisms could tolerate more, the twisting motion would require so much space that one could not pack enough filling yarns in to stabilize the fabric adequately or provide enough strength. Most available leno fabrics are under 10 oz/yd.sup.2. A few have been manufactured in the 10-20 oz/yd.sup.2 range.
The remaining lenos, above 20 oz/yd.sup.2, are rip breakers which have very light weight warps compared to the filling yarns. The rip breakers are used solely to help block the propagation of longitudinal rips.